In a filament type trimmer having a filament storage spool mounted in a rotating housing having a rim portion with an exit aperture through which the filament extends, problems have been found to arise as the result of axial vibration of the filament when the trimmer is running. Such vibration has been found to create rubbing friction between outer turns of filament on the storage spool and the portion of the filament which leaves the spool tangentially and extends to the exit aperture in the rim of the housing. This friction produces heat which may be sufficient to melt the filament locally and produce welding of the filament to itself. This inhibits unwinding of the filament from the storage spool to provide filament advance for replacement of end portions of the filament as they are worn or broken off.
It has also been found that owing to vibration, the outer coils of filament on the spool tend to become entangled with themselves and with inner coils. This likewise interferes with unwinding of filament from the spool to provide filament advance.